The present invention relates to devices for the fixation and/or support of bones. In particular, the present invention relates to a plate for the fixation and/or support of bones of the spinal column. The plate of the present invention has particular application in situations where compressional or xe2x80x9csettlingxe2x80x9d forces, as well as torsional and flexing forces, of xe2x80x9cfixedxe2x80x9d vertebrae on a spinal plate cause significant stressing and potential failure of the spinal plate and/or plate components.
Vertebral fixation has become a common approach to treating spinal disorders, fractures, and for fusion of vertebrae at the time such fixation is instituted. Namely, one or more vertebrae are fixed in position relative to one or more other vertebrae above and/or below the vertebrae to be fixed. Generally, a spinal plate is the device of choice used for mechanically supporting such vertebral fixation. A typical spinal plate includes a plate having a plurality of apertures therethrough. A corresponding plurality of fasteners, i.e., bone screws, are generally positioned into and through respective apertures of the plate to secure the spinal plate to a bone, such as two respective upper and lower supporting adjacent spinal vertebrae. The screws are fastened to the respective support vertebrae to secure the spinal plate to the respective vertebrae. In general, such plate and screw assemblies can be utilized, generally, for anterior fixation of the spine for cervical, lumbar, and/or thoracic fixation.
The basis of anterior fixation or plating is to approach the spine from an anterior or anterio-lateral approach, and use the screws to solidly mount the spinal plate to the affected vertebrae. Often, in addition to the application of a spinal plate, graft material may be combined in attempt to permanently fuse together adjacent vertebrae. The graft material can consist of bone grafts obtained from bones of the recipient or another individual.
A common problem associated with the use of such spinal plates is the tendency of the bone screws to xe2x80x9cback outxe2x80x9d or pull away from the bone into which they are fixed. This problem occurs, primarily, due to the normal torsional and bending motions of the body and spine. This is a particularly important problem because as the screws become loose and pull away from the bone, the heads of the screws can rise above the surface of the spinal plate and, possibly, even work their way completely out of the bone. While this condition can cause extreme discomfort for the recipient, this condition can also create a number of potentially serious physiological problems given the significant amount of nervous and vascular structures associated at or near the potential locations of anterior spinal plate fixations.
A number of designs have been proposed in attempts to prevent screws from pulling away from the bone and/or to prevent the screws from backing out or pulling away from the surface of the spinal plate. Such mechanisms used to prevent bone screws from pulling out of bones include cams which engage and lock the screws, and the use of expanding head screws which expand outwardly when adequate force is applied thereto to engage the holes in the spinal plate. All of these designs have detriments including potential for breakage or requiring particular precision and alignment in their application in order to work correctly. Additionally, loose components and accessories of spinal plates which address the xe2x80x9cbacking-outxe2x80x9d problem can get dropped and/or misplaced while the vertebral fixation surgical procedure is taking place, prolonging and complicating the procedure as well as creating substantial risk of harm to the recipient.
Yet another common problem associated with the use of such spinal plates is the tendency of the vertebrae being xe2x80x9cfixedxe2x80x9d to settle after spinal plate insertion adding compression forces to the above-listed forces which cause the bone screws to xe2x80x9cback outxe2x80x9d or pull away from the bone into which they were fixed. Zdeblick et al. (U.S. Pat. No. 5,324,290) attempted to address the problem of compression forces in the context of treating vertebral burst fractures, but fails to provide any functional means to prevent the screws pulling away as a result of torsional and flexing forces.
Therefore, it is an object of the invention to provide bone fixation apparatus which provides rigid bone-to-bone fixation and/or support, such as e.g. adjacent or second adjacent vertebrae, while allowing post-procedural compression between the respective bones.
It is another object of the invention to provide bone fixation apparatus which affords substantial protection against pulling away of affixing components which may result from torsional movement, flexing movement, or stress and/or dynamic load sharing of the vertebrae, thereby enhancing the bone rebuilding process.
It is yet another object of the invention to provide bone fixation apparatus which attenuates application of stress on the apparatus and affixing components. It is a further object of the invention to provide bone fixation apparatus comprising a support plate and fixation components, and fixation component support which reinforces the fixation components thus to prevent the fixation components from backing out of the support plate.
It is yet a further object of the invention to provide bone fixation apparatus which can be pre-assembled as a loose assembly such that no loose assembly parts or inter-procedural apparatus need be assembled to the assembly during installation of such bone fixation apparatus in a recipient.
In a first family of embodiments, the invention comprehends a bone support plate for use in a bone support assembly. The bone support plate comprises a top surface, a bottom surface opposite the top surface and adapted to engage bone structure of a user; a fixed base portion, having first and second apertures extending therethrough, from the top surface to the bottom surface, for receiving bone fasteners therethrough, and a slot portion, having at least third and fourth apertures extending therethrough, from the top surface to the bottom surface, for receiving bone fasteners therethrough. A first base cover plate recess is disposed in the top surface at the fixed base portion for receiving a base cover plate thereonto and accommodating sliding movement of such base cover plate to impose and withdraw at least partial obstruction of the first and second apertures. Similarly, a second settle cover plate recess is disposed in the top surface at the slot portion for receiving a settle cover plate thereonto and accommodating sliding movement of such settle cover plate to impose and withdraw at least partial obstruction of the third and fourth apertures.
In preferred embodiments, the bone support plate is designed and configured to enable bidirectional sliding movement of a base cover plate connected thereto, wherein the bidirectional sliding movement is in substantial alignment with the top surface of the bone support plate.
Preferably, the bone support plate is designed and configured to enable bidirectional sliding movement of a settle cover plate connected thereto, wherein the bidirectional sliding movement is in substantial alignment with the top surface of the bone support plate.
In some embodiments, the bone support plate comprises a base cover plate fastener aperture extending therethrough, from the first base cover plate recess to the bottom surface of the bone support plate, for receiving a base cover plate fastener therethrough.
In some embodiments, the bone support plate comprises a settle cover plate fastener aperture extending therethrough, from the second settle cover plate recess to the bottom surface of the bone support plate, for receiving a settle cover plate fastener therethrough.
In some embodiments, at least a portion of the bottom surface of the support plate comprises a texturized surface, the texturized surface enhancing engagement of the support plate to the bone structure.
The apertures of the slot portion are preferably longitudinally slot-shaped, with respect to a longitudinal axis of the support plate, to enable respective bone fasteners to be inserted into the respective apertures such that the slot-shaped apertures accommodate movement of the bone support plate with respect to the bone fasteners.
In preferred embodiments, the support plate is curved to conform the support plate to the curvature of corresponding vertebrae.
In a second family of embodiments, the invention comprehends a bone support assembly comprising a support plate, bone fasteners, and a bone fastener cover assembly. The support plate comprises a top surface, a bottom surface adapted to engage such bone structure, a fixed base portion comprising base apertures, and a slot portion comprising slot-shaped apertures. The bone fasteners are disposed in ones of the base apertures and the slot-shaped apertures, the bone fasteners and the support plate, in combination, being adapted and configured for holding the support plate to bone material. The bone fastener cover assembly comprises a cover plate, and at least one cover plate fastener effective to fasten the cover plate to the support plate. The at least one cover plate and the support plate, in combination, accommodate both longitudinal and transverse sliding movement of the cover plate along the top surface of the support plate, with respect to a longitudinal axis of the support plate, to thereby cover and uncover ones of the bone fasteners while the cover plate is attached to the support plate, including uncovering one of a pair of bone fasteners arranged in side-by-side relationship along the longitudinal axis of the support plate, while relatively covering the other of such pair of bone fasteners.
In some embodiments, at least a portion of the bottom surface of the support plate comprises a texturized surface, the texturized surface enhancing engagement of the support plate to bone material.
In preferred embodiments, the slot-shaped apertures are designed and configured to receive respective ones of the bone fasteners into respective slot-shaped apertures such that ones of the bone fasteners can move about freely within the apertures.
Preferably, the cover plate of the bone fastener cover assembly simultaneously covers, at least in part, bone fasteners in at least 4 slot-shaped apertures of the support plate, where one or both longitudinal and transverse movement of the cover plate tends to simultaneously cover a bone fastener in at least one aperture while uncovering another bone fastener in another aperture, whereby at no time are the bone fasteners in all apertures uncovered.
In a third family of embodiments, the bone support assembly comprises a support plate, bone fasteners, a base portion cover assembly disposed at the fixed base portion, and a slot portion cover assembly disposed at the slot portion.
In preferred embodiments, the base portion cover assembly comprises a base cover plate having an upper surface and a lower surface, at least one base cover plate fastener, and at least one base cover plate aperture spanning from the upper surface of the base cover plate to the lower surface of the base cover plate.
Preferably, the size of the at least one base cover plate aperture is greater than a corresponding size of at least one base cover plate fastener by a first dimension greater than or substantially equal to that amount of bidirectional movement of the base cover plate about the base cover plate fastener relative to the support plate necessary to gain fastening access to at least one bone fastener of the support plate while prohibiting fastening access to at least another bone fastener, whereby at no time are all bone fasteners accessible for fastening to the bone structure.
In some embodiments, the at least one base cover plate aperture comprises an aperture wall, wherein an upper portion of the aperture wall comprises an inwardly-tapered frustoconical configuration extending inwardly toward the lower surface of the base cover plate.
In preferred embodiments, the connection of the base portion cover assembly to the support plate is achieved by inserting the base cover plate fastener through the base cover plate aperture of the base cover plate and into a first base cover plate fastener aperture in the support plate, at least a portion of a wall of the first base cover plate fastener aperture being designed and configured to create a locking engagement relationship with the base cover plate fastener, the locking engagement relationship effectively preventing autonomous backing out of the base cover plate fastener from the first base cover plate fastener aperture.
In some embodiments, the locking engagement relationship is formed by the base cover plate fastener, having threading of a first wider pitch, being engaged against the wall of the first base cover plate fastener aperture, having threading of a second narrower pitch, whereby communication between the first and second threadings prevents autonomous backing out of the base cover plate fastener.
In other embodiments, the locking engagement relationship is formed by the base cover plate fastener, having threading, being engaged against the wall of the first base cover plate fastener aperture, comprising a shim or lock-ring having cooperative threading to that of at least a portion of the base cover plate fastener, whereby communication between the base cover plate fastener and the shim or lock-ring of the wall of the first base cover plate fastener aperture prevents autonomous backing out of the base cover plate fastener.
Preferably, the base cover plate overlaps a portion of at least one bone fastener in at least one of the base apertures of the support plate.
In preferred embodiments, the bone support assembly includes a slot in at least one of the base cover plate and the support plate, accommodating sliding of the base cover plate into overlying relationship with first ones of the bone fasteners, and out of overlying relationship with second ones of the bone fasteners.
In preferred embodiments, the base cover plate and the support plate, in combination, are designed and configured to enable bidirectional adjustment of the base cover plate, with respect to the support plate, while maintaining the support plate connected to the base cover plate.
The slot portion cover assembly preferably comprises a settle cover plate having a superior surface and an inferior surface, at least one settle cover plate fastener, and at least one settle cover plate aperture spanning from the superior surface to the inferior surface of the settle cover plate.
In some embodiments, the at least one settle cover plate aperture comprises an aperture wall, wherein an upper portion of the aperture wall comprises an inwardly-tapered frustoconical configuration adjacent the superior surface of the settle cover plate and extending toward the inferior surface of the settle cover plate.
In preferred embodiments, the connection of the slot portion cover assembly to the support plate is achieved by inserting the settle cover plate fastener through the settle cover plate aperture of the settle cover plate, from the superior surface to the inferior surface, and into a second settle cover plate fastener aperture in the support plate, at least a portion of a wall of the second settle cover plate fastener aperture being designed and configured to create a locking engagement relationship with the settle cover plate fastener, the locking engagement relationship effectively preventing autonomous backing out of the settle cover plate fastener from the second settle cover plate fastener aperture.
In some embodiment, the locking engagement relationship is formed by the settle cover plate fastener, having threading of a first pitch, being engaged into the second settle cover plate fastener aperture, having threading of a second pitch, whereby friction between first and second threadings prevents autonomous backing out of the settle cover plate fastener.
In other embodiments, the locking engagement relationship is formed between the settle cover plate fastener and a shim in the second settle cover plate fastener aperture, wherein the shim has cooperative threading to that of the settle cover plate fastener, whereby tension forces between the settle cover plate fastener and the shim of the second settle cover plate fastener aperture prevents autonomous backing out of the settle cover plate fastener.
The settle cover plate preferably overlaps a portion of at least one bone fastener in at least one slot-shaped aperture of the support plate.
In preferred embodiments, the settle cover plate and the support plate are, in combination, designed and configured to enable bidirectional adjustment of the settle cover plate, with respect to the support plate, while maintaining the support plate connected to the base cover plate.
In a fourth family of embodiments, the invention comprehends a method of mounting a support to bone structure. The method comprises providing a herein-described bone support assembly, moving the bone support assembly into position over bone structure to be supported, sliding the base cover plate away from the base apertures and fastening the bone fasteners, disposed in the base apertures, to the bone structure, and sliding the base cover plate at least partially over the bone fasteners disposed in the base apertures and tightening the base cover plate to the support plate thereby to prevent movement of the base cover plate and correspondingly preventing extraction of the bone fasteners in the base apertures.
In preferred embodiments, the method further includes sliding the settle cover plate away from respective ones of the bone fasteners disposed in the slot-shaped apertures and fastening the respective bone fasteners, in the slot-shaped apertures, to the bone structure. In such preferred embodiments, the method also includes sliding the settle cover plate at least partially over the respective fastened bone fasteners and tightening the settle cover plate to the support plate thereby to prevent movement of the settle cover plate, and correspondingly preventing extraction of the fastened bone fasteners.